"Reflective aerosols" refers to microscopic particles in the air that can reflect sunlight back into space, reducing the amount of solar radiation reaching the Earth's surface. Full definition
Let's imagine we force the climate to change by adding some extra energy to the system, perhaps due to an increase in greenhouse gases, or a decrease in reflective aerosols. (atmos.albany.edu)
For aerosols, these emission uncertainties are usually dominant, although for sulfate (an important reflective aerosol) uncertainties in aerosol physics are also substantial. (giss.nasa.gov)
However, a concerted effort to reduce non-CO2 forcings by methane, tropospheric ozone, other trace gases, and black soot might counteract the warming from a decline in reflective aerosols [54], [75]. (journals.plos.org)